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322

PRACTICAL ORGANIC CHEMISTRY'

HINTS   ON    THE    INVESTIGATION    OF   ORGANIC
SUBSTANCES

Provide yourself with a good book of reference, or chemist's

pocket book which contains tables of physical constants.

Homogeneity.  Determine if thesubstanceishomogeneous.

A Liquid.  If it is a liquid, distil a few c.c. from a miniature

distilling flask with a long side-tube, but no condenser, or with

the apparatus shown in
Fig. 86, in which the con-
densing surface is sup-
plied by an inner tube
through which water per-
colates.1

Use a thermometer and
collect the distillate in a
test-tube. Note the boil-
ing-point, and observe if
it fluctuates or remains
constant and if any solid
residue remains. A low
boiling - point generally
denotes a low molecular
weight. A portion dis-
tilling in the neighbour-
hood of 100 may indicate
the presence of water.

It is useful to shake a
known volume (5 c.c.) of
the liquid with an equal
volume of water and to
note if the substance dissolves, or if any marked change in the
volume of the liquid occurs. A convenient apparatus for this

FIG. 86.

This a

If the side pie

pparatus can also be used as reflux condenser or for collecting evolveti gas
piece is furnished with a delivery tube dipping under water or mCrcury.